DESCRIPTION: Complaints with regard to intestinal gas are very common. To date, virtually all studies of intestinal gas have been directed to the study of the readily measured, quantitatively important gases (N2, O2, CO2, H2, and CH4). However, these gases have no odor and are unreactive with tissue. Trace quantities of sulfur-containing gases (H2S, methanethiol, and dimethylsulfide) are produced by colonic bacteria. These gases are extremely malodorous, very reactive with tissue, and have a toxicity comparable to that of cyanide. The physiology and clinical importance of these gases in man has received virtually no study. The overall goal of this project is to obtain the first quantitative data on the production and excretion of these sulfur gases in humans, and then determine the pathophysiological importance of these gases. The specific aims of this proposal are to: 1) Measure the rate of excretion of sulfur-containing gases per rectum and the production of these gases by feces, and determine if the excessive production of these gases results from an abnormality of the bacterial flora or excessive availability of appropriate substrates; 2) Determine if the sulfur containing gases are responsible for the malodor of flatus, and if this condition can be treated via the ingestion of or external use of activated charcoal; 3) Determine if sulfur gas production in the colon can be assessed via measurements of sulfur gases excreted in expired air, and determine to what extent production of sulfur gases in the colon is responsible for halitosis; 4) Determine if the production of sulfur gases is an etiologic factor in the irritable colon syndrome, and if this sulfur gas production can be linked to an abnormality of the colonic flora (either increased sulfate-reducing bacteria or decreased bidifidobacteria); and 5) Determine if enhancing the numbers of fecal bifidobacteria (via feeding of fructooligosaccharides) will decrease sulfur gas production and alleviate the symptoms of the irritable colon syndrome.